Apparatus comprising a particle sorter/dispenser and method therefor

ABSTRACT

A particle sorter/dispenser wherein particles that are suspended in a liquid are flowed through a conduit and selectively dispensed through a dispensing orifice. The conduit includes a sensing zone wherein the liquid-suspended particles are interrogated by a sensor. Data from the sensor is received by processing electronics that analyzes the data from the sensor and makes a decision whether or not to dispense a particle. The particle sorter/dispenser further includes a switch that, responsive to a signal from the processing electronics, controls whether or not a given particle is dispensed through the dispensing orifice. The switch has one or two valves that introduce relatively high-pressure liquid into the conduit. The flow streamlines of the high-pressure liquid controls the flow of the relatively low-pressure liquid-suspended particles in the conduit. Particles that are not dispensed are flowed past the dispensing orifice to a recycle reservoir that depends from the downstream end of the conduit.

STATEMENT OF RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/343,830, filed Oct. 25, 2001, entitled“Apparatus Comprising a Particle Sorter/Dispenser and Method Therefor,”which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to analyzing, sorting anddispensing particles from mixed populations.

BACKGROUND OF THE INVENTION

[0003] Many clinical and biological applications require that smallparticles (e.g., cells, multi-cellular organisms, micro-spheres, etc.)be sorted and dispensed. Small particles can be sorted and dispensedusing a flow cytometer. In a typical flow cytometer, particles areintroduced into a “sheath” fluid that flows into a vertical chamber ortube. The sheath fluid hydrodynamically focuses the particles toward thecenter of the chamber.

[0004] In some flow cytometers, the particles are electrostaticallysorted. For example, in U.S. Pat. No. 6,248,590, the sheath fluid andsuspended particles exit the chamber through a nozzle and free fallthrough open air. In free fall, the sheath fluid breaks up into dropletsthat contain the particles. The droplets pass through a sensing zonewhere the particles are interrogated by a sensor (e.g., optical sensor,etc.). Based on the results of the interrogation, the particles aresorted by diverting them (in either of two directions) or by notdiverting them. The droplets are diverted by: (1) electrically chargingthem and (2) passing them through an electric field. The direction inwhich a charged droplet is diverted depends upon the charge (i.e.,positive or negative) on the droplet. A neutral (i.e., uncharged)droplet falls un-diverted through the electric field. Vessels (e.g.,multi-well plates, etc.) that are appropriately positioned below thechamber receive the diverted and un-diverted droplets.

[0005] In some other flow cytometers, the particles are pneumaticallysorted. For example, in PCT Published Patent Application WO/00/11449,particles that are hydrodynamically-focused by the sheath fluid pass,one-by-one, through a sensing zone that is located within the verticalchamber. There, the particles are interrogated by a sensor. Afterinterrogation, the sheath fluid and particles exit the chamber into openair. A desirable particle, as identified by the sensor and processingelectronics, falls undisturbed (within a droplet) to an underlyingreceiver. In contrast, when undesirable particles are detected, anelectrically-operated valve introduces a flow of compressed gas into thefalling drops of sheath fluid thereby changing the path of thefree-falling sheath fluid and undesirable particles. The diverted fluidand particles are collected in a waste reservoir and recycled, asappropriate.

[0006] These electrostatic and pneumatic flow cytometers suffer from avariety of drawbacks. One drawback is the need for very accurate timing.In particular, to sort particles, the particle-containing sheath fluidmust be diverted—by electrostatics or a blast of gas —at a precise timeafter a particle is detected. Since the time delay is premised on aspecific set of conditions (e.g., flow rate, temperature, flow pattern,etc.), these conditions must be maintained for accurate operation.Consequently, these systems require frequent re-calibration.

[0007] Another drawback of many prior art flow cytometers is that theyare open systems. That is, the sheath fluid and particles are typicallyexpelled into the ambient environment (e.g., air, etc.) before they aresorted. This approach results in a number of processing inefficienciesincluding slow response time, solvent loss due to evaporation and, tothe extent that particles and/or associated moieties (e.g., chemicalspecies attached to the particles, etc.) are oxygen sensitive,degradation.

SUMMARY OF THE INVENTION

[0008] The present invention provides a particle sorter/dispenser andmethod that avoids some of the drawbacks of the prior art.

[0009] In a particle sorter/dispenser in accordance with theillustrative embodiment, the sorting/dispensing portion of the systemhas a non-vertical, and preferably horizontal orientation. Furthermore,the sorting/dispensing portion of the system is substantially liquidfull wherein particles are conducted through the particlesorter/dispenser suspended in a liquid. The speed of the particlesthrough the system is, therefore, controllable. Consequently, the timingissues (e.g., when to divert a particle) that arise in prior-art flowcytometers are far less problematic in a particle sorter/dispenser inaccordance with the illustrative embodiment of the present invention. Inaddition, the processing inefficiencies associated with the openconfigurations of prior art flow cytometers do not plague theillustrative particle dispenser/sorter described herein.

[0010] Some variations of a particle sorter/dispenser in accordance withthe illustrative embodiment of the present invention include a particlereservoir that feeds a particle-containing liquid to a conduit. Theconduit includes a sensing zone wherein the liquid-suspended particlesare interrogated by a sensor. A dispensing orifice, through whichparticles are selectively dispensed to an underlying receiver, isdisposed downstream of the sensing zone.

[0011] Data from the sensor is received by processing electronics. Theprocessing electronics analyzes the sensor data, decides whether or notto dispense a particle, and generates a signal that is indicative of thedecision. The signal is received by a switch. The switch controlswhether or not a given particle is dispensed through the dispensingorifice. Particles that are not dispensed are flowed past the dispensingorifice to a recycle reservoir that depends from the downstream end ofthe conduit.

[0012] In some variations of the illustrative embodiment, the switch hastwo valves—a blocking valve and a dispensing valve. In some othervariations, the switch has only one valve—the dispensing valve.Regarding the two-valve switch, the blocking valve is disposeddownstream of the sensing zone and the dispensing valve is disposeddownstream of the blocking valve and proximal to the dispensing orifice.Each valve independently controls a flow of liquid into the conduit. Theliquid that is flowed through the valves is at a higher pressure thanthe particle-containing liquid already flowing through the conduit.Consequently, the liquid that is flowed through the valves into theconduit controls the flow of the particle-containing liquid that isalready present in the conduit.

[0013] In further detail, when a desirable particle is detected, theblocking valve is opened. A relatively higher-pressure flow of liquidfrom the blocking valve enters the conduit downstream of the sensor andforms a curtain or barrier that the relatively lower-pressureparticle-containing liquid cannot penetrate. As a consequence, anyparticle-containing liquid that has not progressed to the blocking valveis prevented from advancing beyond that point in the conduit.

[0014] Shortly after the blocking valve is opened, the dispensing valveis opened so that a relatively higher-pressure flow of liquid isintroduced into conduit near the dispensing orifice. The liquid thatenters the conduit through the dispensing valve is pressure controlled.The pressure is set so that the flow streamlines of the liquid controlor occupy some but not all of the cross section of the dispensingorifice.

[0015] The flow of liquid through the blocking valve and the dispensingvalve creates a high-pressure region in the conduit. Particles andliquid that are upstream of the blocking valve and/or downstream of theblocking valve cannot enter the high-pressure region and, consequently,will not be dispensed. Any particles downstream of the blocking valveand upstream of the dispensing valve (i.e., within the high-pressureregion) are channeled, along with the higher-pressure liquid, throughthe dispensing orifice to a receiver.

[0016] In some variations of a particle sorter/dispenser in accordancewith the illustrative embodiment, a portion of the conduit is configuredas a venturi. The blocking and dispensing valves are advantageouslylocated in the throat of the venturi. In some variations, the dispensingvalve is located directly across from the open dispensing orifice in a“cross-venturi” arrangement. As a consequence of the pressure profilethrough the venturi, the particle-carrying flow is able to bypass theopen dispensing orifice without exiting (when the dispensing valve isclosed). When the dispensing valve is opened, the relativelyhigher-pressure liquid flowing into the venturi creates flow streamlinesthat lead across the venturi to the dispensing orifice. A particle inthat region of the venturi is channeled by such flow streamlines throughthe dispensing orifice. This cross-venturi arrangement establishes verystable regions of flow, both when the dispensing valve is closed (i.e.,the particle bypasses the dispensing orifice) and when the dispensingvalve is open (i.e., the particle dispenses through the orifice).Furthermore, the flows are quick to re-establish after valve opening orclosing.

[0017] A method in accordance with the illustrative embodiment of thepresent invention includes:

[0018] flowing particles along a first path in a first liquid;

[0019] detecting at least one of the particles;

[0020] flowing, during a first period of time that begins after the oneparticle is detected, a second liquid into the first liquid at apressure that is sufficient to stop particles, other than the oneparticle, from flowing; and

[0021] dispensing the one particle by causing it to deviate from thefirst path.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 depicts a particle sorter/dispenser in accordance with theillustrative embodiment of the present invention.

[0023] FIGS. 2A-2C depict flow patterns in a portion of the particlesorter/dispenser of FIG. 1 as a function of switch operation for aswitch having a single valve.

[0024] FIGS. 3A-3B depict flow patterns in a portion of the particlesorter/dispenser of FIG. 1 as a function of switch operation for aswitch having two valves.

[0025]FIG. 4 depicts a conventional venturi.

[0026]FIG. 5 depicts a particle sorter/dispenser in accordance with theillustrative embodiment of the present invention, wherein the particlesorter/dispenser includes a venturi.

[0027]FIG. 6 depicts a venturi configured for use in conjunction withthe illustrative embodiment of the present invention.

[0028]FIG. 7 depicts a method for particle sorting and dispensing inaccordance with the illustrative embodiment of the present invention.

[0029]FIG. 8 depicts a method for operating a particle sorter/dispenserin accordance with the illustrative embodiment of the present invention.

[0030]FIG. 9 depicts a timing diagram for a switch in particlesorter/dispenser of FIG. 1.

DETAILED DESCRIPTION

[0031]FIG. 1 depicts particle sorter/dispenser 101 in accordance withthe illustrative embodiment of the present invention. Particlesorter/dispenser 101 includes particle reservoir 103, conduit 105,sensor 111, dispensing orifice 115, processing electronics 119, switch123, and recycle reservoir 129, arranged and interrelated as shown.

[0032] As used in this specification, the term “particle” includes,without limitation, biological cells (c.a., 5 to 30 microns indiameter), multi-cellular organisms, such as nematodes, etc. (c.a., 500to 1000 microns) and micro-spheres, as are commonly used forcombinatorial chemistry (c.a., 200 to 450 microns in diameter).Notwithstanding the definition of particle that is provided above, thereis substantially no upper limit on the size of particles that can besorted and dispensed using particle sorter/dispenser 101. That is, avery large particle can be sorted and dispensed via anappropriately-sized version of particle sorter/dispenser 101. The lowerlimit on particle size is dependent on the sensitivity of the detectionmethod (i.e., extinction, fluorescence, light scattering, etc.) and thedetector. With appropriate detection equipment, it is expected thatparticles as small as about 1 micron can be detected.

[0033] In the illustrative embodiment, particle reservoir 103 suppliesparticles 131 for particle sorter/dispenser 101. The particles aresuspended in a liquid so that they can be flowed through conduit 105.Particle reservoir 103 is advantageously pressure controlled. In someembodiments, mixing action is provided, in known fashion, withinparticle reservoir 103 to distribute particles 131 within the liquid.

[0034] Upstream end 107 of conduit 105 receives flow 135 of particles131 and liquid 133 (collectively, “particle-containing liquid 133”) fromparticle reservoir 103. Particles 131 that are flowing through conduit105 are interrogated by sensor 111 in sensing zone 113, which is locateddownstream of upstream end 107. Sensor 111, which is described in moredetail later in this specification, is advantageously capable ofobtaining data that is indicative of the size of particles 131 and/orindicative of other particle characteristics that are deemed to beimportant. Sensor 111 is also capable of generating signal 117 that isrepresentative of the acquired data.

[0035] Processing electronics 119, described in more detail later inthis specification, receives signal 117 from sensor 111 and analyzes thedata carried by signal 117. The data might indicate, for example, thatan interrogated particle meets specification such that it should bedispensed from dispensing orifice 115 to receiver 137. Alternatively,the data might indicate that an interrogated particle does not meetspecification and, consequently, should not be dispensed.

[0036] Processing electronics 119 reaches a decision as to thedisposition of a given particle (e.g., dispense or do not dispense,etc.) based on the data, and generates signal 121 that is indicative ofthe decision. Signal 121 is then transmitted to switch 123.

[0037] Responsive to signal 121, switch 123 affects flow conditionswithin conduit 105. In particular, in one state of switch 123, flowconditions are affected in such a way that at least one particle 131 isdispensed to receiver 137 through dispensing orifice 115. For manyapplications, it is advantageous to dispense only one particle 131 at atime, and particle sorter/dispenser 101 can be operated to do this. Inanother state of switch 123, flow conditions are affected in such a waythat flow 135 of particle-containing liquid 133 bypasses dispensingorifice 115, exits conduit 115 at downstream end 109, and flows intorecycle reservoir 129.

[0038] In some variations of the illustrative embodiment,particle-containing liquid 133 in recycle reservoir 129 is recycled toparticle reservoir 103. In some other variations of the illustrativeembodiment, particle-containing liquid 133 is not recycled. Rather, whenparticle reservoir 103 is empty and recycle reservoir 129 is full, thereservoirs are removed from respective ends of conduit 105 and switched.That is, recycle reservoir 129 is engaged to upstream end 107 of conduit105 while particle reservoir 103 is engaged to downstream end 109. Thoseskilled in the art will be able to make and use particle reservoir 103and recycle reservoir 129 and/or to provide another source of particles131 and liquid 133 for use in particle sorter/dispenser 101.

[0039] In summary, as a function of the operation of sensor 111,processing electronics 119 and switch 123, particle-containing liquid133 that is received by conduit 105 is either:

[0040] (1) dispensed through dispensing orifice 115 and into receiver137, or

[0041] (2) flowed past second end 109 of conduit 105 to recyclereservoir 129.

[0042] The physical configuration and operation of switch 123 is nowdescribed in detail. In some variations of the illustrative embodiment,such as the one depicted in FIG. 1, switch 123 includes two valves:blocking valve 125 and dispensing valve 127. In some other variations ofthe illustrative embodiment, switch 123 includes only one valve:dispensing valve 127. Valves 125 and 127 each (independently) control aflow of liquid into conduit 105. The liquid that is flowed through valve125 can be the same as or different than the liquid that is flowedthrough valve 127. Furthermore, the liquid that is flowed through valves125 and 127 can be the same as or different than liquid 133 in whichparticles 131 are suspended. Typically, a single liquid is used for allof these services. It will be appreciated that the liquid 133 withinparticle reservoir 103 should be inert or otherwise benign to particles131 (and to any chemical species, etc., that are attached or otherwiseassociated with the particles). In some embodiments, the liquid that isflowed through dispensing valve 127 can be reactive. Thus, in additionto dispensing particles 131, particle sorter/dispenser 101 can dispensereactive liquid to receiver 137.

[0043] The flow of liquid through valves 125 and/or 127 affects orcontrols flow 135 of particle-containing liquid 133 through conduit 105.FIGS. 2A-2C illustrate how this occurs for a switch 123 having only onevalve (i.e., dispensing valve 127). These Figures depict a portion ofparticle sorter/dispenser 101 that includes sensor 111, dispensingorifice 115, and dispensing valve 127. In the description that follows,it is assumed that valve 127 is operating in response to signal 121 fromprocessing electronics 119 in the manner previously described.

[0044]FIG. 2A depicts switch 123 in a state in which particle 131 is notdispensed; rather, flow 135 bypasses dispensing orifice 115 and exitsconduit 105 at downstream end 109. In this state, dispensing valve 127is closed so that there is no flow of liquid into conduit 105 throughthe dispensing valve. Flow 135 bypasses dispensing orifice 115 in thisstate because the pressure in conduit 105 at inlet 241 of dispensingorifice 115 is less than the ambient pressure at outlet 243 ofdispensing orifice 115. Advantageously, the pressure at inlet 241 isslightly less than the ambient pressure so that a very small amount ofair is aspirated into conduit 105 through dispensing orifice 115. Thisensures that there will be no leakage of liquid 133 (and particles 131)through dispensing orifice 115.

[0045]FIG. 2B depicts switch 123 in a state in which particle 131 andsome accompanying liquid 133 is dispensed through dispensing orifice115. In this state of the switch, dispensing valve 127 is open so thatflow 245 of liquid is introduced into conduit 105 near dispensingorifice 115. The pressure of flow 245 is controlled so that the flowpattern depicted in FIG. 2B develops. Specifically, flow 245 is directedtoward dispensing orifice 115 such that the streamlines of relativelyhigher-pressure flow 245 control some but not all of the flow throughthe orifice. In other words, a path through dispensing orifice 115remains for relatively lower-pressure flow 135. Particle 131 and someaccompanying liquid 133) flowing through conduit 105 is thereforeconducted, along with flow 245, through dispensing orifice 115.

[0046] In one mode of operation, dispensing valve 127 opens after aspecific time delay to dispense particle 131 and then rapidly closes toensure that only the desired particle(s) is dispensed. The valve timing,which is described in more detail later in this specification, is basedon particle transit time from sensing region 113 to dispensing orifice115. In another mode of operation, pressure is adjusted (reduced)through particle sorter/dispenser 101 to slow flow 135 of particles 131such that valve timing is of decreased significance. In this mode ofoperation, it is advantageous to draw a partial vacuum on recyclereservoir 129 so that particle reservoir 103 can be operated atsub-atmospheric pressure.

[0047]FIG. 2C depicts switch 123 in a state in which flow 135 ofparticle-containing liquid 133 is stopped at a point upstream ofdispensing orifice 115. In this state of the switch, dispensing valve127 is open so that flow 245 of liquid is introduced into conduit 105near dispensing orifice 115. The pressure of flow 245 is controlled sothat the flow pattern depicted in FIG. 2C develops. In this flowpattern, the streamlines of flow 245 completely fill dispensing orifice115 thereby forming a barrier or curtain through conduit 105 at theleading edge of dispensing orifice 115. Since (lower-pressure) flow 135cannot penetrate the (higher-pressure) curtain, a particle 131 flowingthrough conduit 105 toward dispensing orifice 115 is stopped before itcan dispense. The ability to stop a particle in this fashion isparticularly advantageous for assays and other analysis work.

[0048]FIGS. 3A and 3B depict a way in which a switch 123 that has twovalves (i.e., both blocking valve 125 and dispensing valve 127) affectsor controls flow 135 in conduit 105. These Figures depict a portion ofparticle sorter/dispenser 101 that includes sensor 111, dispensingorifice 115, blocking valve 125 and dispensing valve 127. In thedescription that follows, it is assumed that valves 125 and 127 areoperating in response to signal 121 from processing electronics 119 inthe manner previously described.

[0049]FIG. 3A depicts switch 123 in a state in which particle 131 doesnot dispense. In this state, blocking valve 125 and dispensing valve 127are closed so that there is no flow through these valves into conduit105. Flow 135 bypasses dispensing orifice 115 and exits conduit 105 atdownstream end 109. Flow 135 bypasses dispensing orifice 115 in thisstate because the pressure in conduit 105 at inlet 241 of dispensingorifice 115 is less than the ambient pressure at outlet 243 ofdispensing orifice 115.

[0050]FIG. 3B depicts switch 123 in a state in which particle 131 andsome accompanying liquid 133 is dispensed through dispensing orifice115. As previously described, for a switch 123 that has a single valve(i.e., dispensing valve 127), the valve is closed shortly after opening(in one mode of operation) to prevent undesirable particles 131 fromdispensing through dispensing orifice 115. But when switch 123incorporates two valves (i.e., blocking valve 125 and dispensing valve127), the flow of liquid through blocking valve 125, rather than thevalve timing of dispensing valve 127, is advantageously used to preventundesirable particles 131 from dispensing. This mode of operation isdescribed below.

[0051] Assume that particle 131 is interrogated in sensing zone 113 and,based on analysis performed by processing electronics 119, it isdetermined that the particle should be dispensed. After a delay, duringwhich time particle 131 flows from sensing zone 113 past blocking valve125, the blocking valve is opened. Relatively higher-pressure flow 347from blocking valve 125 enters conduit 105 and forms a curtain orbarrier that the relatively lower-pressure flow 135 ofparticle-containing liquid 133 cannot penetrate. Consequently, anyparticle-containing liquid 133 that has not yet reached blocking valve125 is prevented from advancing beyond that point in conduit 105.

[0052] Shortly after blocking valve 125 is opened, dispensing valve 127is opened so that flow 245 of liquid is introduced into conduit 105 neardispensing orifice 115. The pressure of flow 245 is controlled so thatthe flow pattern depicted in FIG. 3B develops. Specifically, flow 245 isdirected toward dispensing orifice 115 such that the streamlines of flow245 control some but not all of the flow through the orifice. Anyparticles 131 downstream of blocking valve 125 and upstream ofdispensing valve 127 are channeled, along with flow 245, throughdispensing orifice 115 to receiver 137.

[0053] Flow 347 of liquid through valve 125 and flow 245 of liquidthrough valve 127 create high-pressure region 349. Particles 131 andliquid 133 that are upstream of valve 125 or downstream of valve 127cannot enter high-pressure region 349 and, consequently, will not bedispensed. For this reason, rapid closure of dispensing valve 127 is notrequired to prevent undesirable particles from dispensing. Furtherdescription of valve timing is provided later in this specification.

[0054] For reliable and proper functioning of particle sorter/dispenser101, a specific pressure profile is desirable, if not required, throughconduit 105, especially in the region near dispensing orifice 115. Inparticular,

[0055] (1) a lower than ambient pressure must be obtained at inlet 241of dispensing orifice 115; and

[0056] (2) the pressure must increase downstream of dispensing orifice115.

[0057] Regarding point (1), having low pressure at the inlet todispensing orifice 115 ensures that particle-containing liquid 133 willsimply bypass dispensing orifice 115, without leakage, when dispensingvalve 127 is closed. Regarding point (2), the increase in pressuredownstream of dispensing orifice 115 ensures that there is enoughpressure to push flow 135 of particle-containing fluid 133 pastdownstream end 109 and into recycle reservoir 129.

[0058] The inventors recognized that the desired pressure profile can beobtained by the well-known venturi configuration. To that end, in somevariations of particle sorter/dispenser 101 in accordance with theillustrative embodiment, a portion of conduit 105 is configured as aventuri.

[0059] A conventional venturi 451 is depicted in FIG. 4. Venturi 451comprises convergent region 453, throat 455, and divergent region 457.Convergent region 453 typically has an included angle of about 21° anddivergent region 457 has an included angle of about 7 to 8°.

[0060] As depicted in FIG. 5, venturi 451 is located downstream ofupstream end 107 and upstream of downstream end 109 of conduit 105. In avariation of particle sorter/dispenser 101 depicted in FIG. 6, sensingzone 113, blocking valve 125 and dispensing valve 127 are disposedwithin (or depend from) throat 455 of venturi 451. In some otherembodiments, sensing zone 113 is disposed upstream of throat 455, suchas in convergent region 453. It is, however, advantageous to locatesensing zone 113 in throat 455 since the cross section for flow isnarrower in throat 455 than in convergent region 453. This reduces therequired coverage area of sensor 111.

[0061] In some variations, such as the one depicted in FIGS. 5 and 6,venturi 451 is formed within material 559, which can be, withoutlimitation, polycarbonate or other materials. Material 559 must be inertto the flowing liquids and particles, and should be suitably stable androbust for machining, etc., to form holes, such as for dispensingorifice 115 and holes 663 and 665 that receive valves 125 and 127.

[0062] Furthermore, material 559 is advantageously visually transparentso that conditions within venturi 451 can be observed. It isparticularly important that material 559 is permeable to electromagneticradiation at the operating wavelength of sensor 111 so that particles131 flowing through sensing zone 113 can be interrogated (for variationsin which sensor 111 is located on the exterior of venturi 451). Foroptical sensors, material 559 can be opaque as long as an optical pathis provided between sensor 111 and the interior of conduit 105 atsensing zone 113. This optical path can be provided, for example, byinserting two lenses (not depicted), such as collimating lenses, throughmaterial 559 at diametrically-opposed regions of sensing zone 113. Oneof the lens places emitter 671 (of sensor 111) in optical communicationwith the interior of conduit 105, and the other lens places detector 673(of sensor 111) in optical communication with the interior of conduit105. In fact, for optical sensing, regardless of whether or not material559 is opaque, collimating lenses are advantageously inserted throughmaterial 559 to minimize optical aberrations, thereby improving theaccuracy of particle detection.

[0063] In the variation depicted in FIG. 6, material 559 is thinned atregion 661 surrounding a portion of throat 455. This allows emitter 671and detector 673 to be situated closer to the liquid flow within venturi451. In the illustration, blocking valve 125 is also disposed withinthinned region 661. In some other variations (not depicted), sensor 111is a fiber-optic sensor wherein a first optical fiber is attached to theemitter and a second optical fiber is attached to the detector. Two verysmall, diametrically-opposed holes are formed through material 559. Thefiber that is attached to the emitter is inserted into one of the holes,and the fiber that is attached to the detector is inserted into theother of the holes. In these variations, region 551 is not included.

[0064] To simplify issues relating to the positioning of emitter 671 anddetector 673, in another variation (not shown) of particlesorter/detector 101, venturi 451 is formed within thin walled tubingthat is shaped into the venturi configuration.

[0065] In some variations of particle sorter/detector 101, the surfacesof conduit 105 facing emitter 671 and detector 673 of sensor 111 areadvantageously flat and parallel to one another, rather than curved asfor a typical cylindrical conduit. Flat surfaces improve the accuracy of(optical) particle detection. In practice, flat, parallel surfaces canbe provided by inserting, within sensing zone 113, a capillary tubehaving a rectangular cross section. Alternatively, the portion of theconduit at sensing zone 113 (e.g., throat 455) can itself be formed witha rectangular cross section.

[0066] With regard to sensor 111, any one of a variety of differenttypes of sensors (e.g., optical, electromagnetic, etc.) is suitable foruse in conjunction with illustrative particle sorter/dispenser 101. Forexample, as to optical sensors, a simple position sensor having emitter671 and photodetector 673 operating at about 850 nm wavelength issuitable. Alternatively, fiber optic sensors, as described above, can beused. Regardless of its specific configuration, sensor 111, inconjunction with suitable processing electronics, is advantageouslycapable of determining the size of particles 131 and is furtheradvantageously capable of determining whether two or more particles arestuck together. Those skilled in the art will be able to suitably selectand operate sensor 111.

[0067] For particle sorter/dispenser 101 that is suitable forsorting/dispensing particles in the 200-1000 micron size range, the flowrate will be such that action should be taken (i.e., a valve should beopened) within about 10 milliseconds after a particle is detected.Consequently, processing electronics 119 is advantageously asuitably-programmed, fast, real-time processor that runs independentlyof a PC operating system (normally the main cause of delays inprocessing data). A suitable microprocessor is the DAP4000/12 fromMicroStar Laboratories of Bellevue, Wash. The processor collects andanalyzes data, and generates a digital or analog signal as a result ofthe data analysis.

[0068] With regard to dispensing orifice 115, in some variations of theillustrative embodiment, dispensing orifice 115 is simply a hole leadingfrom throat 455 to the ambient environment. In some other variations(not depicted) dispensing orifice 115 is implemented as nozzle.

[0069] To cleanly dispense particles 131 to underlying receiver 137,dispensing orifice 115 is advantageously vertical. For ease offabrication, dispensing orifice 115 is formed so that it isperpendicular to throat 455. Consequently, venturi 451 will behorizontal during operation. In some other variations of theillustrative embodiment, venturi 451 is disposed in a non-vertical (butnot horizontal) orientation. In such a variation, dispensing orifice 115is advantageously not perpendicular to throat 455. Specifically, ifventuri 451 is tilted by α degrees relative to the horizontal, theincluded angle between dispensing orifice 115 and throat 455 is 90°-αdegrees.

[0070] As previously described, the operation of switch 123 is dependenton the results of data analysis and decision-making performed byprocessing electronics 119. Further description concerning dataanalysis, decision-making and valve timing is presented in conjunctionwith FIGS. 7-9. These FIGS. and the accompanying description pertain toa switch 123 having both blocking valve 125 and dispensing valve 127. Itwill be clear to those skilled in the art how to modify this teachingfor a switch 123 having a dispensing valve 127 only.

[0071]FIG. 7 depicts a method 700 for particle sorting and dispensing inaccordance with the illustrative embodiment of the present invention.FIG. 8 depicts a method 800 by which method 700 is performed. In otherwords, FIG. 8 depicts a method for operating particle sorter/dispenser101 in accordance with the illustrative embodiment of the presentinvention. And FIG. 9 depicts a timing diagram showing sensor operationand valve timing for practicing methods 700 and 800.

[0072] In accordance with operation 701 of method 700, particles areflowed along a first path in a first liquid. The path is advantageouslynon-vertical, and, more preferably, the path is horizontal. With regardto method 800, operation 701 is implemented by operation 803: closingblocking valve 125 (if it is open from a previous sorting/dispensingoperation). As previously described, when blocking valve 125 is open,flow 347 (FIG. 3B) prevents flow 135 of particle-containing liquid 133from advancing through conduit 105. In the timing diagram depicted inFIG. 9, valve 125 is closed as a final event in the sorting/dispensingoperation. This occurs at T=T3. A particle is depicted flowing towardsensing zone 113 at T=−T1.

[0073] In operation 703 of method 700, at least one of the flowingparticles is detected. Particle detection is depicted as a spike in thedetector trace shown in FIG. 9. Particle detection occurs in sensingzone 113 at T=0. With regard to the operation of sensor 111, thedetection operation involves acquiring a signal having a certain minimumstrength and observing the signal for a certain period of time. If thesignal is observed for less than the expected period of time, it mightindicate that the particle is a fragment of a greater whole, such as,for example, a fragment of a micro-sphere. If the signal is observed fortoo long a period of time, this might indicate that two or moreparticles are stuck together.

[0074] Particle detection is shown as operation 805 of method 800. Valve125 remains closed until a desirable particle is detected. Since, atthis point in the method, valve 125 and valve 127 are closed,particle-containing liquid bypasses dispensing orifice 115 and isreceived by recycle reservoir 129.

[0075] In accordance with operation 705 of method 700, after a desirableparticle is detected, a second liquid is flowed into the first liquid ata pressure that is sufficient to stop particles other than the desirableparticle from flowing. This operation is effected in method 800 byopening blocking valve 125 at operation 807. In the timing diagramdepicted in FIG. 9, valve 125 opens at T=T1. Timing is dependent, ofcourse, on flow conditions. For the particle sorter/dispenser 101described below, and with flows on the order of 0.1 millileter/second,valve 125 opens at about 1-2 milliseconds after detection. Thecorresponding view of particle sorter/dispenser 101 shows liquid flowingthrough valve 125 into conduit 105. As previously described, this flowprevents any particle-containing liquid that is upstream of valve 125from proceeding through conduit 105. Valve 125 is advantageously openedimmediately upon detecting a particle.

[0076] Delays are inherent in the particle sorting/dispensing process(e.g., sensor response time, valve response time, etc.). Therefore, whena single particle is to be dispensed, no particle should trail or lead adesired particle so closely that it cannot be physically segregated(i.e., by the action of valves 125 and 127) from the desired particle.Consequently, a time interval before and after the desired particle isdetected is advantageously checked for the presence of other particles.In accordance with operation 809 of method 800, if particles are presentduring those time intervals, valve 127 remains closed so that none ofthe particles, including the desired particle, dispense.

[0077] In operation 707, the desirable particle is dispensed. Inaccordance with operation 811 of method 800, operation 707 is effectedby opening valve 127 to cause relatively high-pressure liquid to flowinto conduit 105 toward dispensing orifice 115. This flow conducts thedesirable particle through dispensing orifice 115. In the timing diagramdepicted in FIG. 9, valve 127 opens at T=T2. For the aforementioned flowconditions and physical description provided below, valve 127 opens at atime that is about 1-3 milliseconds after T1. After valve 127 has beenopen for a sufficient amount of time to dispense the desirable particle,valve 127 is closed, as per operation 813. In the timing diagramdepicted in FIG. 9, valve 127 closes at T=T3. For the aforementionedflow conditions and physical description of an illustrative particlesorter/dispenser provided below, valve 127 is fully closed at a timethat is about 13-17 milliseconds after T1. Valve opening and closingtakes about 2 millisecs.

Illustrative Particle Sorter/Dispenser

[0078] The size and operating conditions of particle sorter/dispenser101 can be determined as follows. As a “rule-of-thumb,” the diameter ofthe conduit at sensing zone 113 is advantageously less than about fivetimes the size (e.g., diameter, etc.) of particles 131. With thediameter set, the pressure balance is established in conjunction withestablishing the flow rate. For a venturi configuration, the flow rateis adjusted to provide a small amount of aspiration through dispensingorifice 115 within throat 455. This ensures that as long as dispensingvalve 127 is closed, particles flowing through throat 455 will bypassdispensing orifice 115. This provides the minimum flow rate. The flowrate of particle-carrying liquid 133 is limited to a rate that ensuresthat sensor 111 is able to detect particle 131. Of course, as flow rateincreases above the minimum described above, the amount of fluidaspirated by dispensing orifice 115 increases. At some point, the amountof fluid aspirated might become unacceptably high. Consequently, in somecases, the flow rate might be limited by the system's tolerance toaspirated fluid.

[0079] A particle sorter/dispenser configured as described above wasassembled and operated to reliably sort particles. Details of theparticle sorter/dispenser operation follow: Particles: microspheres, 200microns average diameter Liquid: 50:50 isopropyl alcohol:water Particlereservoir pressure:  1.5 psig Recycle reservoir pressure:    0 psigThroat diameter: 0.024 inches Dispensing orifice diameter: 0.024 inchesBlocking valve size:  0.05 inches Dispensing valve size:  0.05 inchesPressure of Liquid through valves: 25-30 psig Flow rate though throat:0.1-1 milliliter per second

We claim:
 1. An apparatus comprising: a conduit having a first end and asecond end, wherein said first end and said second end are in fluidiccommunication and said first end of said conduit receives a flow of afirst liquid that contains particles; a sensor that detects saidparticles in a sensing zone of said conduit, wherein said sensing zoneis downstream of said first end and upstream of said second end; adispensing orifice that dispenses some of said particles that aredetected by said sensor, wherein said dispensing orifice is disposeddownstream of said sensing zone and upstream of said second end of saidconduit; and a switch that, responsive to said sensor, controls the flowof said first liquid and particles through said conduit, wherein: in afirst state of said switch, at least one of said particles is dispensedthrough said dispensing orifice; and in a second state of said switch,said particles bypass said dispensing orifice and exit said conduit fromsaid second end thereof.
 2. The apparatus of claim 1 wherein said switchcomprises an dispensing valve that is disposed downstream of saidsensing zone and proximal to said dispensing orifice.
 3. The apparatusof claim 2 wherein, when said switch is in said first state, saiddispensing valve opens to a first position causing a second liquid toflow into said conduit at a pressure that establishes a flow pattern insaid conduit that directs said one particle to flow through saiddispensing orifice.
 4. The apparatus of claim 2 wherein, when saidswitch is in said second state, said dispensing valve is closed.
 5. Theapparatus of claim 2 wherein, when said switch is in a third state, saiddispensing valve opens to a second position causing a second liquid toflow into said conduit at a pressure that establishes a flow pattern insaid conduit that prevents said one particle from reaching saiddispensing orifice.
 6. The apparatus of claim 2 wherein said switchfurther comprises an blocking valve that is disposed downstream of saidsensor region and upstream of said dispensing valve.
 7. The apparatus ofclaim 6 wherein, when open, said blocking valve causes a third liquid toflow into said conduit at a pressure that establishes a flow pattern insaid conduit that prevents the flow of said first liquid and saidparticles from flowing past said blocking valve.
 8. The apparatus ofclaim 1 wherein said conduit comprises a convergent region that isdisposed downstream of said first end, a throat that is disposeddownstream of said convergent region, and a divergent region that isdisposed downstream of said throat and upstream of said second end. 9.The apparatus of claim 8 wherein said sensing zone is in said throat.10. The apparatus of claim 8 wherein said dispensing orifice is disposedin said throat.
 11. The apparatus of claim 8 wherein said convergentregion, said throat, and said divergent region are disposed in anon-vertical orientation.
 12. The apparatus of claim 1 furthercomprising a reservoir that contains said first liquid and saidparticles, wherein said reservoir is in fluidic communication with saidfirst end of said conduit.
 13. The apparatus of claim 1 furthercomprising a reservoir that receives said particles and said firstliquid that bypass said dispensing orifice, wherein said reservoir is influidic communication with said second end of said conduit.
 14. Anapparatus comprising: a venturi, said venturi having a convergentregion, a throat, and a divergent region; a sensor that detectsparticles in a sensing zone in said venturi, wherein said particles flowin a first liquid that enters said venturi via said convergent region; adispensing orifice that dispenses some of said particles that aredetected in said venturi by said sensor, wherein said dispensing orificeis disposed downstream of said sensing zone; and an dispensing valvethat is located downstream of said sensing zone and proximal to saiddispensing orifice, wherein said dispensing valve controls the flow of asecond liquid into said venturi, and wherein the flow of said secondliquid causes at least one of said particles that are detected in saidsensing zone to be dispensed through said dispensing orifice.
 15. Theapparatus of claim 14 wherein said dispensing orifice dispenses saidparticles from said throat and said dispensing valve delivers the flowof said second liquid into said throat.
 16. The apparatus of claim 14,further comprising an blocking valve that is located downstream of saidsensing zone, upstream of said dispensing valve and upstream of saiddispensing orifice, wherein said blocking valve controls the flow of athird liquid into said venturi.
 17. The apparatus of claim 16 whereinthe flow of said third liquid prevents said particles and said firstliquid from flowing past said blocking valve toward said dispensingvalve.
 18. The apparatus of claim 14 wherein said sensor is an opticaldetector.
 19. The apparatus of claim 12 wherein said venturi is disposedin a substantially horizontal orientation.
 20. An apparatus comprising:a conduit having a first end and a second end, wherein said first end ofsaid conduit receives a flow of particles that are suspended in a firstliquid; a sensor that senses said particles in a sensing zone of saidconduit; a dispensing orifice that dispenses said particles from saidconduit, wherein said dispensing valve is located downstream of saidsensing zone and upstream of said second end; and an dispensing valvethat is disposed downstream of said sensing zone, proximal to saiddispensing valve and upstream of said second end wherein: saiddispensing valve controls the flow of a second liquid into said conduit;said second liquid is at a higher pressure than said first liquid insaid conduit such that the flow of said second liquid is sufficient tocontrol the flow of said first liquid and said particles in saidconduit.
 21. The apparatus of claim 20 wherein said conduit ishorizontal.
 22. The apparatus of claim 20 further comprising an blockingvalve that is disposed downstream of said sensing zone, upstream of saiddispensing valve, and upstream of said dispensing orifice, wherein, whensaid blocking valve is open, a high pressure region is created in saidconduit downstream of said blocking valve so that particles that areupstream of said blocking valve are prevented from entering said highpressure region.
 23. The apparatus of claim 20 wherein said particlesare cells.
 24. A method comprising: flowing particles along a first pathin a first liquid; detecting at least one of said particles; flowing,during a first period of time that begins after said one particle isdetected, a second liquid into said first liquid at a pressure that issufficient to stop said particles, other than said one particle, fromflowing; and dispensing said one particle by causing it to deviate fromsaid first path.
 25. The method of claim 24 wherein said first path isnon-vertical.
 26. The method of claim 24 wherein the operation ofdetecting further comprises determining if one or more additionalparticles were detected in a first interval of time before said oneparticle is detected.
 27. The method of claim 24 wherein the operationof detecting further comprises determining if one or more additionalparticles were detected in a second interval of time after said oneparticle is detected.
 28. The method of claim 24 wherein the operationof dispensing further comprises flowing, during a second period of timethat begins after said one particle is detected, a third liquid intosaid first liquid, wherein: said third liquid is flowed into said firstliquid at a location downstream of where said second liquid is flowedinto said first liquid; and said third liquid is flowed at a pressurethat is sufficient to cause said one particle to deviate from said firstpath.
 29. The method of claim 24 wherein the operation of detectingfurther comprises determining if one or more additional particles weredetected in a first interval of time before said one particle isdetected, and further comprising the operation of stopping the flow ofsaid third liquid when one or more additional particles are detected insaid first interval of time.
 30. The method of claim 24 wherein theoperation of detecting further comprises determining if one or moreadditional particles were detected in a second interval of time aftersaid one particle is detected, and further comprising the operation ofstopping the flow of said third liquid when one or more additionalparticles are detected in said second interval of time.
 31. The methodof claim 28 wherein the operation of dispensing further comprisescollecting said one particle in a receiver.
 32. A method comprising:flowing particles in a first liquid in a conduit; detecting at least oneof said particles in said conduit; creating a region of high pressure insaid conduit after said one particle is detected, wherein the onedetected particle is in said region of high pressure; and dispensingsaid one particle from said region of high pressure.
 33. The method ofclaim 32 wherein said region of high pressure is created after a firstinterval of time elapses after said one particle is detected, whereinthe operation of creating said region of high pressure further comprisesflowing a second liquid into said first liquid, wherein said secondliquid is at a higher pressure than said first liquid.
 34. The method ofclaim 33 further comprising removing said region of high pressure byending said flow of said second liquid, wherein said region is removedafter a second interval of time elapses, wherein said second timeinterval provides sufficient time for said one particle to be dispensedthrough a nozzle from said region of high pressure.
 35. The method ofclaim 33 wherein said region of high pressure is created after a firstinterval of time elapses after said one particle is detected, whereinthe operation of creating said region of high pressure further comprisesflowing, at two separate locations along said conduit, a second liquidand a third liquid into said first liquid, said separate locationsdefining the boundaries of said high pressure region, wherein saidsecond liquid and said third liquid are at a higher pressure than saidfirst liquid.
 36. The method of claim 35 further comprising removingsaid region of high pressure by: ending said flow of said third liquidafter a second interval of time elapses, wherein said second interval oftime provides sufficient time for said one particle to be dispensed fromsaid region of high pressure through a nozzle; and ending said flow ofsaid second liquid after a third interval of time elapses, wherein saidthird interval of time is longer than said second interval of time. 37.The method of claim 32 wherein said operation of dispensing furthercomprises sorting said particles based on results of said detecting,wherein some of said particles are dispensed and some are not.
 38. Themethod of claim 37 wherein a first group of said particles that aredispensed are collected in a first receiver based on said results, and asecond group of said particles that are dispensed are collected in asecond receiver based on said results.
 39. A method comprising:detecting a particle; flowing said particle along a horizontal path intoa flow-controlled region; and establishing a first flow pattern thatprevents additional particles from entering said flow controlled region.40. The method of claim 39 further comprising establishing a second flowpattern that causes said one particle to dispense from saidflow-controlled region.
 41. The method of claim 40 wherein said particleflows in a first liquid, and wherein said operation of establishing afirst flow pattern comprises flowing a second liquid into a firstliquid.
 42. The method of claim 40 wherein said operation ofestablishing a second flow pattern comprises flowing a third liquid intosaid first liquid.